Cisco DHCP Relay Agent Configuration with GNS3


DHCP Relay Agent is used to forward, requests and replies between DHCP Server and DHCP Client if DHCP server resides in another network than client. In this Cisco DHCP Relay Agent GNS3 Example lesson, we will configure DHCP Relay Agent on Cisco routers. Our DHCP Server will be in another network and we will use “ip-helper address” command to configure DHCP Relay Agent and forward requests and replies.


We will use the below topology consist of two routers, one switch and one PC for our DHCP example.




For our Cisco DHCP Relay Agent Configuration on GNS3, we will follow the below steps one by one.


  • IP Addressing
  • Static Routing Configuration
  • DHCP Server Configuration on Router_2
  • DHCP Relay Agent Configuring on Router_1
  • Default Route Configuration on Router_1 and Router_2


So, let’s start our example.


You can also download GNS3 Labs


IP Addressing

Firstly, let’s configure ip addresses of the interfaces on the routers. Here, we ill configure one interface on Router_2 and two interfaces on Router_1.


Router_2# configure terminal

Router_2(config)# interface GigabitEthernet0/0

Router_2(config-if)# ip address

Router_2(config-if)# no shutdown


Router_1# configure terminal

Router_1(config)# interface GigabitEthernet0/0

Router_1(config-if)# ip address

Router_1(config-if)# no shutdown

Router_1(config-if)# interface GigabitEthernet0/1

Router_1(config-if)# ip address

Router_1(config-if)# no shutdown



Static Routing

To teach network (other interface network of Router_1), we need to use a static route through this network on Router_2. After that, we will ping to test the static route.


Router_2(config)# ip route

Router_2(config)# end

Router_2# ping



DHCP Server Configuration

After ip addressing and static routing, we will start to do DHCP related configurations. Here, Router 2 will be our DHCP Server. So, firstly, we will configure DHCP Relay Agent on Router 2. We will use “ip dhcp pool pool-name” command to create a DHCP Pool. Then we will specify the pool range. After configuring the default router address for the hosts, we will configure DNS Server address.


Out DHCP Pool name will be IPCISCO and the ip pool range will be We will use as default router address for the clients.


Router_2(config)# ip dhcp pool IPCISCO

Router_2(dhcp-config)# network

Router_2(dhcp-config)# default-router

Router_2(dhcp-config)# dns-server



DHCP Relay Agent Configuration

After configuring DHCP Server on Cisco Router, Router_2, now we came to the key part of this configuration lesson. This is Cisco DHCP Relay Agent Configuration. We will configure Router_1 as a DHCP Relay Agent which will forward DHCP request and replies between DHCP Server and DHCP Host.


Here, we will use the IP address of the DHCP Server with “ip helper-address” command on Router_1. This ip address will be, the interface ip address of the Router_2.


Router_1(config)# interface GigabitEthernet0/1

Router_1(config-if)# ip address

Router_1(config-if)# ip helper-address


You can check also DHCP Packet Tracer Example



After our Cisco DHCP Relay Agent Configuration on GNS3, now it is time to verify our configuration. To do this, we will check the ip address of the PC. And we will see the ip address that is assigned by DHCP server from DHCP Server pool range.




On DHCP Server, we can check DHCP bindings with “show ip dhcp bindings” command. Here, we will see PC MAC number with assigned ip address.




We can also check dhcp pool configuration with “show ip dhcp pool” command.


Router_2# show ip dhcp pool


Utilization mark (high/low) : 100 / 0

Subnet size (first/next) : 0 / 0

Total addresses : 254

Leased addresses : 1

Excluded addresses : 0

Pending event : none

1 subnet is currently in the pool

Current index IP address range Leased/Excluded/Total – 1 / 0 / 254


In this GNS3 Configuration Example, we have configured Cisco DHCP Relay Agent on GNS3.


Back to: CCNP Enterprise 350-401 ENCOR > DHCP and DNS

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